Polymer dispersions derived from vinyl esters and monomers copolymerizable therewith and their use as binders for paints and plasters are known and have already been described many times. Such polymer dispersions are typically prepared by emulsion polymerization; with the polymerization being effected in one or more stages. In the polymerization processes which have become known to date, monomer mixtures are converted by free-radical polymerization by addition of initiators in the presence of protective colloids and/or emulsifiers.
U.S. Patent Application Publication No. 2009/0069495 to Fichtner et al. (“Fichtner”) is directed to coating compositions comprising binders based on polyvinyl ester dispersions prepared by a multistage polymerization process. In a first stage, a polyvinyl ester dispersion is prepared by polymerizing at least one vinyl ester of a saturated carboxylic acid (and optionally further monomers copolymerizable therewith) in the presence of at least one emulsifier and/or at least one protective colloid. In a second stage, monomers in a dissolved form, a pure form, or in the form of an emulsion are added to the reaction mixture and polymerized. The polyvinyl ester dispersions of Fichtner comprise polymerized silanes and/or epoxides, and are said to offer high weathering resistance when used in plasters, exterior coatings, like façade paints and wood protection paints and dispersion based paints. However, the dispersions of Fichtner suffer from the disadvantage of producing coatings with high water permeability (w-value).
U.S. Patent Application Publication No. 2009/0203814 to Petri et al. (“Petri”) discloses multistage polymers derived from hard and soft monomer compositions containing vinyl esters, of which at least one monomer composition must contain an unsaturated organosilicon compound. The dispersions of Petri are suitable for the formation of solvent-free coating materials which exhibit little foam formation and are said to offer improved blocking resistance, gloss and abrasion resistance in coatings produced therewith. However, the dispersions of Petri suffer from the disadvantage of a high dirt pick behavior when those dispersions are used in exterior façade paints and exterior plasters.
U.S. Patent Application Publication No. 2007/0244238 to Desor et al. (“Desor”) is directed to polymer dispersions prepared by emulsion polymerization containing at least two copolymers, A and B, with glass transition temperatures differing by at least 10° C. In emulsion polymerization, usually one or more emulsifiers are used. Attempts have been made to avoid the use of alkylphenol ethoxylates (“APEO”) as nonionic emulsifiers due to health and environmental concerns. Accordingly, Desor's dispersions either contain no alkylphenol ethoxylates (“APEO”), or contain such small amounts thereof to be suitable for the preparation of wood varnishes, glazes and gloss paints. An APEO-free emulsifier is also provided by Desor, which ensures a desired shear stability of multistage polymer dispersions, and does not adversely affect the blooming and water resistance of the dispersion. However, the emulsions described in US 2007/0244238 display insufficient fire retarding properties when those emulsions are used in plaster formulations for thermal insulation systems, especially external insulation finishing systems (EIFS),
U.S. Pat. No. 7,078,455 to Heldmann et al. (“Heldmann”) is directed to aqueous plastic material dispersions based on vinyl ester copolymers. More particularly, Heldmann's dispersion is based on a vinyl ester copolymer having a solid content of up to 80% by weight substantially stabilized by ionic components, and a minimum film formation temperature (MFFT) of less than 20° C. However, the dispersions of Heldmann suffer from the disadvantage of a high dirt pick behavior when the dispersions are used in exterior façade paints and exterior plasters.
Notwithstanding the availability of the above types of polymer dispersions, there remains a persistent need for polymer dispersions which offer enhanced performance over existing compositions when used in, for example, paints and plasters. As an example, a significant disadvantage of coatings for use in exterior façade paints and plasters is high water permeability, measured as w-value according to DIN EN 1062-3. Therefore, it would be useful to provide polymer dispersions capable of use in, for example, paints and plasters, that offer reduced water take up, without loss of properties in other performance areas, like fire retardant properties.
The present invention addresses these and other needs by providing polymer dispersions for use in, for example, paints and plasters, which offer enhanced wet scrub resistance, enhanced color retention, low water take up (w-value), low dirt pick up, high color retention and superior fire retardant properties. More specifically, the present invention is directed to vinyl ester-ethylene acrylic dispersions prepared in a multistage polymerization process involving at least a first stage and a second stage. Moreover, the dispersions can be formulated into coating compositions without the use of coalescent agents, which is important for producing low VOC coatings
Films and coatings formed from these polymer emulsions exhibit low dirt pick up and color retention and at the same time have a low w-value. This w-value can be determined according to DIN EN 1062-3. In addition, films and coatings formed from the present polymer emulsions exhibit good fire retardancy and high wet scrub resistance. Further the emulsions are coalescent free and allow low volatile organic compound formulation process capability.